The invention relates to a photogalvanic cell based upon light-sensitive materials in solution.
It is known that there exist certain light-sensitive materials for which electrochemical equilibrium in electrolyte solutions is strongly influenced by light. The electrochemical energy state of the materials in darkness is significantly increased upon excitation by photons. It is further known that practical advantage may be taken of this phenomena in a photogalvanic cell, which is a conventional device comprising a set of electrodes immersed in an electrolyte solution containing such light-sensitive materials. When the solution in the vicinity of one electrode in the photogalvanic cell is irradiated with light while the solution in the vicinity of a second electrode is maintained in darkness, the different energy states of electrochemical equilibrium in the light and dark portions of the solution cause a potential difference to be observed between the light and dark electrodes. Furthermore, shifts in electrochemical equilibrium at the electrodes generate an electrical current which may be withdrawn from the cell. in principle, the photogalvanic cell based on light-sensitive materials in solution can be used indefinitely, as its function depends only upon reversible shifts in equilibrium in the cell solution in response to light energy, and no material within the cell is consumed as fuel.
Such photogalvanic cells based upon light-sensitive materials in solution are to be distinguished from photovoltaic cells based on inorganic semiconductors, which are purely solid state electronic devices, from photogalvanic cells with light-sensitive electrodes, and from fuel generating cells such as those producing the decomposition of water into H.sub.2 and O.sub.2 which can be removed and stored as a fuel supply.
The conventional photogalvanic cell based on light-sensitive materials in solution typically comprises an aqueous electrolyte solution containing an organic dyestuff, a metal redox couple, and a common acid. The instant invention specifically relates to the addition to the electrolyte solution in such photogalvanic cells of one or more complexing agents for the higher valent ion of the metal redox couple present. It has been previously proposed to add a complexing agent to a mixture of a photo-reducible dyestuff and a metal redox couple. (See K. G. Mathai and E. Rabinowitch, J. Phys. Chem. 66 (1962), p. 663). However, this earlier work was concerned with the irreversible storage of energy through separation of high energy state products by precipitation of the metal ion complex, not with the use of such agents in a reversible photogalvanic cell.